A method is proposed in which, with respect to lesions such as an origin of arrhythmia or atherosclerosis, an electrode for delivery of radiofrequency energy is arranged inside an elastic balloon, and a radiofrequency electric field is radiated therefrom, to provide thermotherapy to a tissue in contact with the balloon (for example, refer to Patent Document 1).    Patent Document 1: Japanese Unexamined Patent Publication No.: 2005-177293
In order to provide uniform thermotherapy to a target site to be treated inside a blood vessel and a heart, it is necessary to bring a balloon into close contact with the target site and then block a blood flow to thereby selectively heat and ablate the target site. According to the conventional balloon catheters, however, a wall thickness of the balloon is uniform, and thus there is concern of isolating a site different from the target site. Further, thermal energy inside the balloon leaks from a portion that is not in contact with the target site, resulting in poor heating efficiency.
Furthermore, there has been a problem that a position of the target site is subjected to changes by a pulsation of the heart and the blood flow, and thus it is difficult to bring the balloon into close contact with the target site only by pressurizing the inside of the balloon to change a diameter of the balloon.
With the view of the problems described above, it is, therefore, an object of the present invention to provide a balloon catheter system which enables only the target site to be effectively ablated, enabling the balloon to be brought into close contact with the target site by conforming to a shape of the target site.